Influence of dietary component manipulation and feed management strategies on growth and rumen development of weaned dairy heifers
Well-developed replacement heifers provide a central foundation for the continued success of the dairy industry. Emphasis on improving pre-weaned calf nutrition has predominated in the industry, but opportunities exist to improve post-weaning heifer nutrition and management. We aimed to evaluate common feed management strategies seen in the industry and their effects on growth, feed efficiency (G:F), and rumen development of calves from birth to 8 mo of age using pen- and individually-fed animal trials. Little information exists regarding post-weaning performance and rumen development of calves fed conventional or high planes of nutrition pre-weaning; therefore, we evaluated two milk replacer feeding programs with two post-weaning diets differing in non-fiber carbohydrate (NFC) content. Overall, calves fed a high plane of nutrition pre-weaning with a low NFC post-weaning diet were 9.8 kg and 12.4 kg lighter than calves fed low or high planes of nutrition pre-weaning, respectively, with a high NFC post-weaning diet. Additionally, average daily gain (ADG) and frame height were increased for high NFC-fed animals regardless of pre-weaning treatment. Rumen development with respect to tissue morphology was similar between pre-weaning planes of nutrition in 12 wk old calves. However, 28 wk old animals previously fed a conventional milk replacer program had 20% greater papillae surface area compared to calves fed a higher plane of nutrition pre-weaning. Interestingly, rumen papillae morphology was similar between post-weaning diets and no interaction of pre- with post-weaning diet was observed. However, in a concurrent study evaluating low and high NFC diets using pen-fed heifers, feeding low NFC diets with added fat resulted in higher ADG and G:F compared to heifers fed high NFC diets despite similar dietary ME and CP content. Overall, these results suggest feeding diets with highly digestible carbohydrates to promote greater G:F and skeletal growth post-weaning, particularly when higher planes of nutrition are provided pre-weaning. As G:F improved when NFC and starch increased in the diet, we investigated increasing dietary concentrate proportions for growing heifers and the effects when switched to a high forage diet. Heifers fed 80% concentrate were the heaviest, tallest, and most feed efficient during the treatment period, but exhibited decreased in performance when switched to a high forage total mixed ration (TMR; 60% hay) compared to heifers previously fed 60% or 40% concentrate. Additionally, molar proportions of propionate and butyrate were greater when heifers were fed 80% or 60% concentrate, potentially influencing rumen development. Delivering of feed as a TMR is common practice on dairy operations, as nutrients are delivered consistently with increased labor efficiency. Additionally, ensiled forages are commonly included as the primary forage component in heifer diets, although growth and intake responses when feeding ensiled forages as compared to hay are limited and inconsistent. We compared feeding a common diet delivered by feeding hay and concentrate separately (HF), hay side-dressed with concentrate (SBS), and a TMR, observing that G:F of HF- and SBS-fed heifers was 8 to 10% greater overall compared to heifers fed a TMR. Additionally, HF-fed heifers were 13.5 kg heavier at the end of the study and had 5.6% greater DMI overall compared to SBS- and TMR-fed heifers. We also fed weaned heifers diets using mixed grass/legume forage preserved as hay or baleage as the only forage source to evaluate growth and efficiency. Heifers fed hay were 6.7 kg heavier than heifers fed baleage at the conclusion of the study. Heifers fed hay also consumed more DM and tended to have greater G:F than heifers fed baleage. As G:F was affected by forage preservation, feed delivery method, and carbohydrate inclusion in growing heifer diets, we postulated that rumen development may not be as mature as previously believed for heifers post-weaning. Greater understanding of the effects of feed management strategies on growing heifer performance has been achieved from our research, allowing more precise feeding recommendations and development of feeding programs to improve heifer development.
Nennich, Purdue University.
Animal sciences|Nutrition|Veterinary services
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